why only tungesten is used as a filament of bulb?

Answer 1

It isn't the only material for light filaments but it is the most used material.

The lamp industry represents the largest commercial application of tungsten wire. It is used in this application because it displays excellent creep resistance at elevated temperatures. Tungsten is an attractive lamp filament material because it has an extremely high melting temperature (~3,695 K) and a low vapour pressure at high temperatures. Tungsten is also intrinsically brittle and, initially, this prevented the manufacture of tungsten wire. But advances in metallurgy enabled tungsten wire and coil filaments to be handled without breakage, so tungsten became the backbone of the whole incandescent lamp industry.